Citation: Doubabi, H.; Salhi, I.; Essounbouli, N. A Novel Control Technique for Voltage Balancing in Bipolar DC Microgrids. Energies 2022, 15, 3368. https://doi.org/10.3390/ en15093368 Academic Editor: Luis Hernández-Callejo Received: 21 March 2022 Accepted: 28 April 2022 Published: 5 May 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). energies Article A Novel Control Technique for Voltage Balancing in Bipolar DC Microgrids Hajar Doubabi 1,2, * , Issam Salhi 3 and Najib Essounbouli 1 1 CReSTIC, Reims University, 9 rue de Québec B.P 396, 10026 Troyes, France; najib.essounbouli@univ-reims.fr 2 CISIEV, Faculty of Sciences and Technology, Cadi Ayyad University, Marrakesh40000,Morocco 3 FEMTO-ST Institute, University Bourgogne Franche-Comté, UTBM, CNRS, Rue Thierry Mieg, 90000 Belfort, France; issam.salhi@utbm.fr * Correspondence: hajardoubabi@gmail.com Abstract: The bipolar DC microgrid topology is characterized by three voltage levels and is able to transfer power more efficiently than a conventional DC microgrid. This paper proposes an advanced control strategy aiming to ensure the voltage balancing between the upper and lower terminals of a bipolar DC microgrid regardless of the distribution of loads. The proposed controller is based on the backstepping method, which is well known for its the robustness and the global asymptotic stability that can be guaranteed for the system. A particle swarm optimization algorithm has also been adopted for an optimal design of the proposed controller parameters. Simulation results in a Matlab/Simulink environment has been presented to verify the effectiveness and reliability of the proposed voltage-balancing controller. Keywords: voltage balancing control; bipolar DC microgrid; three-level DC–DC step-up converter 1. Introduction A microgrid has been defined according to CORDIS Europe as an advanced electric system formed of a series of electrical loads, power source elements (photovoltaic (PV) systems, fuel cells, wind turbines, etc.) and storage (batteries, flywheel, compressed air, etc.) connected to the local grid through a single point of connection The microgrid integrates management strategies controlling both the energy flow within the microgrid itself and the interchange of power with the supply grid [1]. One of the most important features of microgrids is that they are able to operate in two modes: the grid-connected mode and the islanded (off-grid) mode [2]. Microgrids can be built in rural and urban areas at multiple scales: low (such as a house/building with PV panels), medium (such as a factory) and large (such as a big university campus [3]). Over the last two decades, significant progress has been made in DC/DC power converters, energy storage technologies (batteries, supercapacitor, etc.) and DC-based dis- tributed energy resources (solar photovoltaics, fuel cell, etc.) [4]. In addition, an increasing number of DC-consuming devises such as LEDs, televisions, monitors and computers have been integrated into buildings. In addition, and new emerging technologies such as electric vehicles are DC [4]. Therefore, DC microgrids have become an attractive option and present a promising alternative to the AC counterpart. Various research studies have been focused on comparing the DC and AC microgrids [5–7]. It has been revealed that DC microgrids can transmit significantly more energy through distribution lines and require fewer power conversion stages, which decrease not only losses but also costs. DC microgrids present higher levels of power quality that are strongly intertwined with voltage stability. Moreover, DC microgrid control is simpler as there is no need for frequency synchronization and reactive power management. Despite the multiple merits of DC microgrids [8], appropriate control and safe design is always needed to avoid potential issues and maximize their benefits [4]. Energies 2022, 15, 3368. https://doi.org/10.3390/en15093368 https://www.mdpi.com/journal/energies